netdev - Re: [PATCH v2 bpf-next 0/4] bpf: Improve verifier test coverage on sparc64 et al.

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Message-ID: <20181201055501.xi5b45mkc775gf3w@ast-mbp.dhcp.thefacebook.com>
Date:   Fri, 30 Nov 2018 21:55:02 -0800
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     David Miller <davem@...emloft.net>
Cc:     daniel@...earbox.net, ast@...nel.org, netdev@...r.kernel.org
Subject: Re: [PATCH v2 bpf-next 0/4] bpf: Improve verifier test coverage on
 sparc64 et al.

On Fri, Nov 30, 2018 at 09:07:54PM -0800, David Miller wrote:
> 
> On sparc64 a ton of test cases in test_verifier.c fail because
> the memory accesses in the test case are unaligned (or cannot
> be proven to be aligned by the verifier).
> 
> Perhaps we can eventually try to (carefully) modify each test case
> which has this problem to not use unaligned accesses but:
> 
> 1) That is delicate work.
> 
> 2) The changes might not fully respect the original
>    intention of the testcase.
> 
> 3) In some cases, such a transformation might not even
>    be feasible at all.
> 
> So add an "any alignment" flag to tell the verifier to forcefully
> disable it's alignment checks completely.
> 
> test_verifier.c is then annotated to use this flag when necessary.
> 
> The presence of the flag in each test case is good documentation to
> anyone who wants to actually tackle the job of eliminating the
> unaligned memory accesses in the test cases.
> 
> I've also seen several weird things in test cases, like trying to
> access __skb->mark in a packet buffer.
> 
> This gets rid of 104 test_verifier.c failures on sparc64.
> 
> Changes since v1:
> 
> 1) Explain the new BPF_PROG_LOAD flag in easier to understand terms.
>    Suggested by Alexei.
> 
> 2) Make bpf_verify_program() just take a __u32 prog_flags instead of
>    just accumulating boolean arguments over and over.  Also suggested
>    by Alexei.
> 
> Changes since RFC:
> 
> 1) Only the admin can allow the relaxation of alignment restrictions
>    on inefficient unaligned access architectures.
> 
> 2) Use F_NEEDS_EFFICIENT_UNALIGNED_ACCESS instead of making a new
>    flag.
> 
> 3) Annotate in the output, when we have a test case that the verifier
>    accepted but we did not try to execute because we are on an
>    inefficient unaligned access platform.  Maybe with some arch
>    machinery we can avoid this in the future.
> 
> Signed-off-by: David S. Miller <davem@...emloft.net>

The patch 2 didn't apply as-is to bpf-next, since I applied your earlier fix
"bpf: Fix verifier log string check for bad alignment" to bpf tree.
So I applied that fix to bpf-next as well and then pushed your series on top.
I think git should do the right thing when bpf and bpf-next trees converge.
But... let me know if I should drop that fix from bpf tree...
just to be on a safe side.